Microtome Cross-Section
Definition
A thin section of a paint chip cut perpendicular to the layer planes, allowing each layer to be examined separately by microscopy and microspectroscopy.
- Cut orientation
- Perpendicular to paint layer planes
- Purpose
- Isolate individual layers for separate analysis
- Follow-on techniques
- Microscopy, FTIR, Py-GC-MS
- Evidence type
- Paint chip
Common questions
Why cut across the layers rather than examine the chip whole?+
A paint chip viewed from the surface only shows the topmost layer; cutting a cross-section exposes the full layer stack, including primer and undercoats, whose sequence and count are often more discriminating between vehicles than surface colour alone.
What can layer sequence reveal that surface colour cannot?+
A manufacturer's specific paint system, including primer type, colour coat, and clear coat number and order, can narrow a chip to a make, model range, or repaint history, information invisible without exposing the layer structure.
Related terms
- ASTM E2937
- ASTM International standard guide for identification of paint binders by pyrolysis-GC-MS; specifies pyrolysis conditions, GC column, oven program, and diagnostic ion reporting.
- ATR (Attenuated Total Reflectance)
- An FTIR sampling mode in which the sample is pressed against a diamond or ZnSe crystal and the evanescent wave probes the...
- Backscattered Electron (BSE) Imaging
- An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after...
- ENFSI EPG Protocol
- European Network of Forensic Science Institutes Expert Working Group on Paint protocol; the European standard for paint comparison examination sequence and reporting.
- FTIR Microspectroscopy
- Fourier-transform infrared spectroscopy collected from a microscope-focused spot of 10-20 µm diameter; the primary technique for paint binder characterisation.
- IRUG Database
- Infrared and Raman Users Group spectral database; covers historic pigments, artists' materials, and museum-object coatings. Primary reference for art-investigation paint analysis.
- Likelihood Ratio Reporting
- A Bayesian framework for reporting paint-comparison conclusions, expressing the probability of the observed data given the hypothesis of common source versus the...
- Py-GC-MS
- Pyrolysis gas chromatography mass spectrometry. Thermal decomposition of a paint sample, separation of fragments, mass spectral identification. Definitive identification of polymer binders.
- Pyrogram
- The gas chromatographic trace of volatile fragments produced by pyrolysis of a polymer; acts as the polymer-class fingerprint in Py-GC-MS.
- Raman Microspectroscopy
- A vibrational spectroscopy technique using a focused laser beam to excite molecular vibrations in an ink sample. Non-destructive. Primary method for toner...
- SEM-EDS
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy; provides elemental composition of each paint layer at 1-5 µm spatial resolution.